1. Field of the Invention
This invention relates generally to magnetic disk cartridges in which a disc-shaped, thin magnetic recording medium, namely a magnetic disc sheet, is rotatably supported. More particularly, the invention relates to a magnetic disc cartridge in which a liner is placed in sliding contact with the magnetic disc sheet to protect and clean the sheet.
2. Description of the Related Art
Magnetic disk sheets, i.e., floppy disks, are widely used as recording media for computers because they are easy to handle and low in cost. A conventional magnetic disk sheet comprises a disk-like base sheet made of flexible polyester or the like, and magnetic material layers overlaid on opposite surfaces of the disk-like base sheet. The magnetic disk sheet is rotated for magnetically recording information on the magnetic material layers by use of a magnetic head.
In general, writing of information on the magnetic disk sheet or reading of information therefrom is carried out by rotating a magnetic disk sheet and, at the same time, sliding a magnetic writing head or a magnetic reading head over the magnetic recording surface in the radial direction of the magnetic disk sheet. Therefore, when conformity of the surface of the magnetic disk sheet with the magnetic head is low, or when dust or the like enters the gap of the magnetic head in the course of writing or reading of the information, the signal input and/or signal output fluctuates, or drop-outs occur. Such fluctuations or drop-outs are serious because magnetic disk cartridges are used mainly as digital data memories in computers or the like and a single data error may be unacceptable.
Referring to FIG. 1, a conventional 3.5-inch type small magnetic disk cartridge 10 will be described. The cartridge 10 includes an outer case formed of an upper casing 11, a lower casing 12, and a dust-preventing shutter 13. The shutter 13 covers openings 14 and 15 in the casings 11 and 12, respectively, and has an opening 13a to permit access to a recording surface of a magnetic disk sheet 16 by a magnetic recording head. A hub 16a is fixed to the magnetic disk sheet 16 for rotatably driving the disk sheet 16 with a disk drive mechanism.
Disk-like liners 17 and 18 formed of a rayon nonwoven fabric, a polyester nonwoven fabric or the like are disposed between the magnetic disk sheet 16 and an inner wall surface of the upper and lower casings 11 and 12, respectively. The liners 17 and 18 lightly contact the upper and lower recording surfaces of the magnetic disk sheet 16, respectively. A lifter spring 19 is attached to the lower casing 12 to exert pressure against the liner 18 to maintain contact between the liners 17 and 18 and the recording surface. When the magnetic disk sheet 16 is rotated, the liners 17 and 18 function to remove dust or the like from the surface of the magnetic disk sheet 16.
As mentioned above, liners formed of rayon, polyester or the like have heretofore generally been shaped in a disk-like form. This disk-like shape requires a significant amount of material for the liner, and also results in a large amount of material being wasted during the manufacturing process. For example, several disk-shaped liners may be cut from a single sheet of liner material. A disk-shaped liner will require an amount of material, both used and wasted, having a surface area equivalent to a square with sides equal to a diameter of the liner. Thus, a conventional disk liner having a diameter of 8.6 cm requires approximately 74 cm.sup.2 (8.6 cm.times.8.6 cm) of liner material to manufacture. This large amount of liner material is a significant cost in high volume disk cartridge production. Moreover, conventional disk-shaped liners require a large amount of thermal welding to secure the liners to the plastic casings.
In addition, the large amount of textile liner material within the disk cartridge has a tendency to create what is referred to as "soft error." Soft error results from textile particles from the liners being leaked to the media of the rotating magnetic disk sheet. Such soft error is primarily caused by the ultrasonic welding of the upper and lower plastic casings 11 and 12 together during manufacture. The ultrasonic welding utilizes a high frequency vibration, which tends to break the liner material down and cause the material to be leaked to the media. The soft error will generally correct itself after the disk rotates a sufficient number of times so that the leaked particles of liner material are reabsorbed by the liners. However, if the recording head contacts the disk sheet while a large amount of liner material is in the media, permanent damage to the media can result.
Accordingly, there is a need for an improved liner for floppy disk cartridges to reduce the occurrence of soft error and to minimize manufacturing costs.